I. Field
The following description relates generally to communication systems, and more particularly to an SDMA operation and message system for a plurality of stations.
II. Background
In order to address the issue of increasing bandwidth requirements that are demanded for wireless communications systems, different schemes are being developed to allow multiple user terminals to communicate with a single access point by sharing the channel resources while achieving high data throughputs. Multiple Input Multiple Output (MIMO) technology represents one such approach that has recently emerged as a popular technique for the next generation communication systems. MIMO technology has been adopted in several emerging wireless communications standards such as the Institute of Electrical Engineers (IEEE) 802.11 standard. IEEE 802.11 denotes a set of Wireless Local Area Network (WLAN) air interface standards developed by the IEEE 802.11 committee for short-range communications (e.g., tens of meters to a few hundred meters).
In communication systems, medium access (MAC) protocols are designed to operate to exploit several degrees of freedom offered by the air link medium. The most commonly exploited degrees of freedom are time and frequency. For example, in the IEEE 802.11 MAC protocol, the “time” degree of freedom is exploited through the CSMA (Carrier Sense Multiple Access). The CSMA protocol attempts to ensure that no more than one transmission occurs in a neighborhood of potential high interference. The “frequency” degree of freedom can be exploited by using different channels.
Recent developments have led to space dimension being a viable option. Spatial Division Multiple Access (SDMA) can be used for improving utilization of the air link by scheduling multiple terminals for simultaneous transmission and reception. Data is sent to each of the terminals using spatial streams. For example, with Spatial Division Multiple Access (SDMA) a transmitter forms orthogonal streams to individual receivers. Such orthogonal streams can be formed because the transmitter has several antennas and the transmit/receive channel consists of several paths. The receivers may also have one or more antennas (MIMO, SIMO). For this example, it is assumed that the transmitter is an access point (AP) and the receivers are stations (STAs). The streams are formed such that a stream targeted at STA-B, for example, is seen as low power interference at STA-C, STA-D, . . . , etc., which will not cause significant interference and not be ignored. In order to form the orthogonal streams, the AP needs to have the channel state information (CSI) from each of the receiving STAs. The channel state information can be measured and communicated in several ways. The use of CSI will facilitate the configuration of the SDMA streams.
Consequently, it would be desirable to address one or more of the deficiencies described above.